Proven thermoelectric generator technology is well founded in scientific literature and has been satisfying small portable electrical power needs, such as fans, battery chargers and devices that can be used near a heat supply. However, despite its wide application there are several problems with today's thermoelectric devices that must be addressed.
Thermoelectric Generators (Seebeck Effect) have had little impact on supplying electrical power needs for today's world with a Zt factor near one. The Zt factor describes a mathematical relationship between electrical power output and the high temperature Th and cold temperature Tc of available heat sources. A Zt factor of three is required to make thermoelectric generated power competitive on a commercial scale.
Besides the low Zt factor for converting of power, the constant expanding and contracting of the hot and cold layers of a thermoelectric device create cracks in the soldered layers that results in efficiencies dropping off and eventual failure to the device. The operating temperature of today's devices is also limited below optimum operating temperatures by the use of low temperature solders. Lower temperatures within the interface layers results in a lower electric power output from the generator assembly. The low temperature solders Tin (Sn) 95% Antimony (Sb) 5% commonly used in today's devices, re-melt at 235 degrees C., much below the melting point of Bismuth Tellurium Alloys of 650 degrees C. The low operating temperatures with consequent lower interface temperatures make thermoelectric device efficiencies lower.
Still other problems plaguing today's thermoelectric generator industry are the very low output voltages with high output currents. Attempts have been made to make larger, heavier thermoelectric generators to increase voltage, however this had just the opposite result with short life cycles and lower power yields. The larger units have created uneven heat distribution with larger bulky heat sinks and higher internal electrical resistance. These larger units had the opposite result with lower voltage and power yields diminishing in the life cycle of the unit. The use of micron and submicron particles formed by powder metallurgical processes known in the art have had increased power factors, but still much below commercial levels.
There has been recent success by Boston College and MIT (U.S. Pat. No. 7,465,871) to increase the Zt factor with nanometer size composite thermoelectric materials. Still the first major development in 50 years of research of thermoelectric devices has had little use in bringing thermoelectric power generators to a commercial level. It is widely theorized that the smaller the particle size of thermoelectric Bismuth Tellurium alloys the greater the thermoelectric effect. This is understood to be a positive relationship between phonon scattering and good electrical conductivity. It is understood that an ideal thermoelectric device is one that has poor heat (phonon) conduction with very good electrical (electron) conductivity.